(i) Field of the Invention
The present invention relates to a speed changing apparatus usable for a small car inclusive a car having three or four wheels adapted to move on any rugged ground, each of the cars being steered by means of a bar-shaped handle and having a gear for backward movement.
(ii) Description of the Prior Art
To facilitate understanding of the invention a typical conventional speed changing apparatus will be described below with reference to FIGS. 6 to 9.
FIG. 6(A) is a front view of a conventional car having four wheels adapted to move on rugged ground or land and FIG. 6(B) is a plan view of the car in FIG. 6(A). The car 1 is equipped with ballon tires 2 on both the front and rear axles which are filled with compressed air at a lower pressure. FIG. 7 is a schematic view illustrating how main components are arranged in the speed changing apparatus for the conventional saddle riding type car having three or four wheels or motorcycle. FIG. 8 is a partial sectional view of the speed changing apparatus taken in line VIII--VIII in FIG. 7 and FIG. 9 is a fragmentary sectional view of the speed changing apparatus taken in line IX--IX in FIG. 7. In the conventional speed changing apparatus as illustrated in FIGS. 7 to 9 rotational force of the crank shaft 5 is transmitted to a counter shaft 6 via a driving gear 5a, a gear 6a meshing with the former and a clutch mechanism (not shown) and rotational force thus transmitted to the counter shaft 6 is then transmitted to an auxiliary shaft 7, for instance, via a driving gear 6b and a driven gear 7a meshing with the former. Further, rotational force thus transmitted to the auxiliary shaft 7 is outputted from a driving shaft 8 as required rotational force via speed changing gears on the auxiliary shaft 7 and speed changing gears both on the driving shaft 8 and the counter shaft 7 meshing with the first mentioned speed changing gears in dependence on selection of the speed changing gears on a change cam 9.
Some small car of the above-mentioned type are provided with a gear for backward movement in the speed changing apparatus. The speed changing apparatus usable for a small car of the above-mentioned type is generally constructed such that shifting of gears in the speed changing mechanism is controlled by rotational displacement of a rotary type change cam 9 and the rotational position of the latter is selected by means of a foot pedal. To control shifting of the gear for backward movement the speed changing apparatus is additionally equipped with a separate shifting device and an actuating member. Operation of the actuating member is carried out after the change cam is displaced to the neutral position. Due to the arrangement of the speed changing apparatus made in that way, it is complicated in structure and handling is achieved only with many difficulties. In a modified speed changing apparatus the change cam is additionally formed with another cam groove to control shifting of the gear for backward movement. In this case one of the forward movement stages is selected by rotating the change cam by means of the one actuating member and the backward movement stage is selected by rotating the change cam by means of the same actuating member. This type of arrangement leads to an advantageous feature that structure and handling of the speed changing apparatus are simplified. However, it is found that this type of conventional speed changing apparatus has a drawback in that teeth on the gears are damaged or injured when the gear for backward movement is shifted unintentionally without sufficient preliminary confirming as to what speed stage is assumed by the apparatus at this moment, because the latter is so constructed that speed changing is successively carried out by repeating the same steps.